The present invention relates to a sealed storage battery, especially a sealed storage battery that includes a large number of cells and is used as a high-voltage, large-capacity emergency power source, as well as to a modular-type battery system assembly for accommodating the sealed storage battery therein.
High-voltage, large-capacity storage batteries are used for the back-up power source of, for example, the telephone switchboard and the computer, and the power source for emergency lighting. With a view to simplifying the maintenance, the use of sealed lead-acid storage batteries that take advantage of the oxygen cycle, in which gaseous oxygen evolved in the course of charging is absorbed by the negative electrode, has been increasing for such applications. A number of the large-capacity storage batteries, however, have a large total weight, which results in increasing the required parts of a battery system for accommodating the batteries therein, complicating its structure, and thereby raising the manufacturing cost of the battery system.
The battery evolves heat in use. In the case where a plurality of batteries are used in the form of a battery assembly, the heat remains and hardly diffuses on the central portion. The battery located near the center is accordingly worked at a higher temperature than the batteries located outside. Namely there is a difference in working environmental temperature between the batteries located inside and outside. The temperature difference results in a difference in properties between the batteries. Such difference is accumulated when the batteries are used over a long time period. This adversely affects the reliability of the power source system. The temperature difference is further increased when a plurality of the battery assemblies are laid one upon another to constitute a high-voltage battery system assembly.
In order to dissipate the heat evolved in the battery and eliminate the adverse effect of the temperature difference, one proposed structure has ribs extending in the longitudinal direction on the outer surface of the battery container to define spaces between the battery container of the adjoining battery (for example, Japanese Laid-Open Utility Model Publication No. Hei 6-54192). When the plurality of batteries are arranged in the sidelong orientation, the spaces defined by the ribs of the adjoining batteries are made parallel to the outer surfaces of the battery containers. In this case, the heat evolved in the battery assembly can not be dissipated upward by the air current.
In one proposed modular system for accommodating batteries to solve the above problem, a plurality of batteries are laid one upon another in such a manner that terminals are located on the left and right sides of the modular system and each battery is inserted in a space defined by a top plate, supporting columns, and a bottom plate (Japanese Laid-Open Patent Publication No. Hei 6-89706). Since the batteries are laid one upon another, there is no empty space between the adjoining upper and lower batteries. This arrangement does not allow the heat evolved in use, especially in the course of charging, to be dissipated. When the batteries are used over a long time period, a significant difference tends to occur between the properties of the batteries included in the modular system. The power source system is generally charged with a constant voltage. A gradual increase in temperature of the battery accordingly lowers the charging voltage of the battery. This may cause release of the heat that increases the charging current and thereby result in fatal failures.